Io
Io is the innermost of Jupiter’s four Galilean moons and the third-largest moon of Jupiter.
Io is the innermost of Jupiter’s four Galilean moons and the third-largest moon of Jupiter. It is the most volcanically active world in the Solar System, with hundreds of volcanoes driven by tidal heating from Jupiter and neighbouring moons. Io was discovered by Galileo Galilei in 1610.
Discovery and naming
Io was discovered by Galileo Galilei in 1610 during his observations of Jupiter’s moons. The name Io comes from Greek mythology and was later adopted as the moon’s standard name.
Orbit and physical characteristics
Io orbits very close to Jupiter and completes one orbit in about 42.5 hours. It is slightly larger than Earth’s Moon and is among the densest moons in the Solar System.
Volcanism and geology
Io is the most volcanically active world in the Solar System. Its surface is continually resurfaced by volcanic eruptions, lava flows, and sulfurous deposits, leaving relatively few impact craters.
Atmosphere and surface composition
Io has a very thin atmosphere, mainly composed of sulfur dioxide. Its surface contains sulfur and silicate materials, producing distinctive yellow, red, white, black, and green colouring.
Key facts
- Io is one of Jupiter’s four Galilean moons, along with Europa, Ganymede, and Callisto.
- It is the innermost of the Galilean moons and the third-largest moon of Jupiter.
- Io’s surface is shaped by extreme volcanism, with hundreds of volcanoes and active lava fountains.
- Its activity is powered by tidal heating caused by gravitational interactions with Jupiter, Europa, and Ganymede.
- Io was first observed by Galileo Galilei on 8 January 1610.
Io is a major object of interest for Canadian astronomy education and public science outreach because it is a nearby, well-studied example of tidal heating and active volcanism in the Solar System.
Frequently asked questions
What is Io?
Why is Io so volcanically active?
Who discovered Io?
How big is Io?
Does Io have an atmosphere?
References
- NASA Science — https://science.nasa.gov/jupiter/jupiter-moons/io/facts/Supports: Discovery date, volcanic activity, Galilean moon status, size relative to Earth's Moon, orbital position.
- NASA Science — https://science.nasa.gov/jupiter/jupiter-moons/io/Supports: Most volcanically active world, tidal heating explanation, lava fountains, lava lakes, general overview.
- The Planetary Society — https://www.planetary.org/worlds/ioSupports: Innermost Galilean moon, volcanic activity, atmosphere composition, orbital and physical context.
- Encyclopaedia Britannica — https://www.britannica.com/place/Io-satellite-of-JupiterSupports: Discovery by Galileo, innermost Galilean moon, naming context, volcanic activity.
- European Space Agency — https://sci.esa.int/web/hubble/-/39830-the-volcanic-moon-ioSupports: Sulfur dioxide frost, extremely tenuous atmosphere, discovery context, volcanism observations.